Typical footwear often comprises a midsole attached to the upper along a periphery of the sole, so as to create a cavity into which a user's foot is placed, and a wear surface attached to a bottom surface of the midsole. Because the wear surface is usually in contact with the ground, the midsole is often made of a material that is softer than the wear surface but, because the midsole should resist breaking down while providing structural integrity, shock absorption, and support to the shoe, the midsole is generally tougher than cushioning material. In other types of footwear, the midsole and wear surface are combined and such combination is usually called an outsole.
Whether a shoe uses a midsole or outsole, consumers often use comfort as at least one basis for purchasing a particular shoe over a competitor's shoe. Therefore, manufacturers have longed to improve comfort of their shoes, which is often achieved by placing resilient or cushioning material between a user's foot and a top surface of the midsole or outsole, both of which are hereinafter generally defined as a sole. However, due to repeated foot strikes, particularly in the heel and balls of the foot areas, the cushioning material often breaks down or becomes flattened. In some cases, the breakdown of the cushioning is so severe that the user may discard the shoe even though other parts of the shoe are usable.
Furthermore, by merely adding more cushioning material to a shoe, the likelihood of retaining moisture and/or bacteria in the cushioning material is also increased. Therefore, adding cushioning may also disadvantageously introduce odors or fungi.
In some other types of footwear, grooves in the sole were provided to enhance comfort. U.S. Pat. No. 3,087,261 (Russell), U.S. Pat. No. 3,087,262 (Russell), U.S. Pat. No. 4,638,577 (Riggs), U.S. Pat. No. 4,658,514 (Shin), and U.S. Pat. No. 4,498,251 (Shin) seem to relate to soles with grooves for enhancing comfort or flexibility. However, the grooves do not appear to extend substantially across a width of the shoe because doing so would negatively affect stability or support. As a result, the shoe may not have optimal comfort or flexibility due to the possible introduction of instability.
Similarly, U.S. Patent No. to Aoki seems to have holes in a heel to enhance flexibility or comfort but the holes do not substantially traverse across the entire width of the shoe. Again, the shoe may not have optimal comfort or flexibility due to the possible introduction of instability.
Both U.S. Pat. No. 3,079,708 to Hack and U.S. Patent Publication No. 2002/0189132 to Yamamoto seem to relate to shoes having grooves for enhancing comfort or flexibility but, because the grooves are so large, the grooves themselves may offset the comfort or flexibility that they provide. These references may employ a covering for the grooves to provide an even surface for the user. However, such a covering may reduce overall flexibility of the shoe.
What is desired, therefore, is a shoe having improved comfort and flexibility. Another desire is a shoe having optimal comfort and flexibility without sacrificing stability. A still further desire is to reduce bacteria or moisture accumulation in the shoe while optimizing comfort and flexibility.